In recent years an increasing number of new cars are being sold with built-in rear view cameras. Lawmakers have called for all new vehicles to be sold with rear view cameras built in. The interest in rear view cameras arises from the danger that a driver, when backing a vehicle, may not see all that is behind the vehicle. Indeed, each year there are several fatalities brought about when a vehicle backs over an individual that was not seen by the driver. Additionally, damage is done to property and vehicles behind a driver when the driver backs up without seeing an obstacle behind them.
Typically there are several blind zones around a vehicle. For example, in most vehicles the driver cannot see what is below the rear view window and immediately behind the vehicle. If the driver backs up without having first walked behind the vehicle and checked what is back there the possibility exists that a person or object of value will be injured or damaged.
In order to assist the driver, rear view cameras are now installed in many new vehicles. These cameras give the driver a view of what is behind the vehicle at the time they begin backing up so that they will see anything that is in the path of the vehicle and be able to stop before something is damaged. However, there are millions of older vehicles and still some new vehicles that will be driven but which will have no such driver assisting camera.
User installable rear view cameras can be purchased online or through retail outlets. Typically these camera systems will include a camera and a monitor. The camera is installed in the user's bumper by drilling a hole in the bumper and then feeding a power wire inside the vehicle and connecting to the vehicle's reverse light wiring. The monitor is attached to the dash and connected to a power source such as the vehicle's power port. A video cable from the camera is connected to the video input of the monitor.
In order to install such a camera the user must follow a number of difficult steps which include risks of damaging their vehicle or even possibly voiding certain vehicle warranties. In order to overcome some of these difficulties and dangers, some cameras can be attached to the vehicle's license plate, avoiding the need to drill a hole in the bumper. For these cameras, a small hole may still have to be drilled in the car's body somewhere which will allow passage of the power cable. The cable must then be connected to the car's electrical system by splicing into the reverse light wiring or otherwise electrically connecting the camera's power wiring to the car's power wiring.
In many vehicle cameras a wire connects the video output signal of the camera to the video input port of a monitor. This approach provides a high quality delivery of video to the monitor. However, it requires routing of the video cable from the camera, which is typically on the outside and at the rear of the vehicle, to the monitor, which is inside and in front of the driver area. In order to hide the cable from view or at least keep it from being snagged or pulled by movements inside the car, it is common to route the cable beneath the vehicle's carpet and upholstery and teed it through other areas where it will be secure and out of sight. This is a difficult and time consuming task. It can be avoided, however, through the use of wireless transmission to deliver the video signal from the camera to the monitor. If the video signal is transmitted wirelessly by radio to the monitor, there is no need to route a video cable through the vehicle, though most often a power cable must be routed into the vehicle and attached to a radio transmitter that must also be connected to the vehicle's electrical system.
Backup cameras are most useful when a vehicle is backing up. For this reason, a backup camera is configured to be activated when the vehicle is in reverse. After-market backup cameras are typically powered by connecting to the vehicles reverse light wiring. Thus, when the vehicle is in reverse, and the reverse lights come on, power is delivered to the camera and it begins to transmit video data to a connected human interface device which is typically a monitor. Unfortunately, it is difficult for a typical user to make this connection to the reverse light wiring. It is difficult to determine which wires to connect to and what polarity to connect to them with, and to splice into these wires in a neat fashion without damaging the wiring.
In order to avoid the need to connect a power cable from the camera to the vehicle, it is of interest to use batteries to power the camera. Battery powered cameras are widely used in other applications and have been for decades. In order to conserve battery power, low power components, techniques and protocols are employed in the design. With no connection to the reverse light wiring, a battery powered camera would have the limitation of not being turned on automatically when the vehicle is in reverse. This is a limitation that would need to be overcome if a battery powered camera is to be useful.
In a battery powered camera system it is common to find a user operated switch that will turn the camera on or off so that it is only on when in use. By keeping it off when not in use, battery power is conserved. In some systems a user operated switch turns the camera on and off. When the user wants to use the camera, they must turn the switch on, and then when they have finished using the camera, they must turn the switch off in order to conserve battery power.
Some vehicle cameras use such a user-operated switch. The camera, for example, may be kept in a storage compartment until needed at which time the user takes the camera from the storage compartment, mounts it in a position where it is useful (such as pointing at the ball of a trailer hitch-and-ball system) and then turns on the switch. The camera can then deliver image data to a monitor. When the task has been completed, the user can then turn the camera off and return the camera to storage. A disadvantage of this approach is that the user must perform the multiple steps of removing from storage, mounting, switching on, returning to the driver's seat to operate the vehicle, then switching off, unmounting, and returning the camera to storage. If the user forgets to turn the camera on there will be the need for the driver to go back to the camera, switch it on, and return the driver's seat. If the user forgets to shut it off when storing it, the camera's batteries will run down.
In order to maximize the benefits of a battery powered camera for a vehicle, it would be desirable to have the batteries last long enough so that the camera can be mounted and left in place for many months of use. Then on the rare occasions when the batteries have run down and need to be recharged or replaced, the camera can be temporarily unmounted for battery replacement, or connected to a power source for battery charging.
Accordingly, there is a need to minimize battery power consumption in the camera.
There is also a need to design a camera that is easy to install and doesn't require drilling holes or routing wires.
There is also a need to activate the camera when the vehicle is in reverse or when the driver otherwise needs the camera.
A well-known technique for conserving power in battery powered sensors is often called Duty Cycling. A survey of different types of Duty Cycling systems is found in [Maheswar et al., “A Survey on Duty Cycling Schemes for Wireless Sensor Networks”, IRACST—International Journal of Computer Networks and Wireless Communications (IJCNWC) Vol. 3, No 1. February 2013; incorporated herein]. In this technique a radio is mostly in a low power state where it can neither transmit nor receive. Periodically, however, the radio is turned on briefly to listen for a transmitted signal or to transmit a signal and listen for a response. A timer is used to determine the period of the listen cycle. Duty Cycling is widely used in wireless sensor networks. An example of an application of duty cycling is in [Polastre et al., “Versatile Low Power Media for Wireless Sensor Networks”, SenSys '04 Proceedings of the 2nd International Conference on Embedded Networked Sensor Systems, pp. 95-107, Nov. 3-5, 2004, Baltimore, Md. USA; incorporated herein].
A disadvantage of duty cycling is that parts of the system such as the radio are periodically brought to a fully ‘on’ state so that the radio can listen. Although the ‘on’ time of the duty cycle can be much shorter relative to the ‘off’ time, power consumption during the ‘on’ time accumulates over time toward discharging the battery. Still, because that consumption rate is much less than if the radio were on always, duty cycling is a useful approach in some applications to conserving battery power.
A second disadvantage of duty cycling is that the radio can only respond to transmissions during the time when it is on. Therefore, most of the time there is a delay that occurs between the time that a base station starts transmitting to a duty cycled radio and when the radio reaches the ‘on’ portion of the duty cycle and turns on to receive and respond to such transmissions.
U.S. Pat. Nos. 7,507,946 and 7,420,149 refer to a network sensor system wherein multiple wireless battery powered cameras are accessed by a hub that is connected to the Internet. In each camera, power is provided by a battery. In order to conserve battery power, duty cycling is used. In this specific implementation of duty cycling, a processor and radio are kept in a low power ‘sleep’ state. The processor can, however, still respond to processor interrupt requests (IRQs). These interrupts can come from internal timers and other internal functions or from external signals connected to the processor's interrupt request lines. Because the processor's interrupt handling capability is still functional, it can recognize which of several possible sources the interrupt came from and begin executing an interrupt subroutine customized for that specific interrupting source. The interrupt hardware can advantageously recognize the source of the interrupt and cause the processor to change its program counter such that it diverts its execution to an interrupt subroutine.
U.S. Pat. Nos. 7,507,946 and 7,420,149 also describe the use of a timer that activates a radio from time to time in a duty cycling scheme designed to reduce power consumption in a network imager. The low power timer runs continuously between cycles where the radio and other circuitry are briefly activated. U.S. Pat. Nos. 7,507,946 and 7,420,149 call for the timer to interrupt the microprocessor, which means interrupt responsive circuitry must consume enough power to remain active during the low power portion of the duty cycle. Because microprocessors typically come equipped with low power timers, this can be implemented without adding an additional timer.
A disadvantage of this approach is that because the timer and the part of the processor handling interrupts must be powered on, the processor is not completely off and will continue to consume power, albeit at a much lower level than when the processor is executing instructions. A second disadvantage is, as discussed above, that there will often be a delay between the time that a base station starts transmitting and when the network sensor system turns on, receives the transmission, and responds.
In summary, U.S. Pat. Nos. 7,420,149 and 7,507,946 teach of a viable way to conserve power in a home surveillance system. However, they consume power to operate a timer and interrupt handling capability and to periodically activate a radio to listen as part of a duty cycled scheme. They also incur a delay in response time as a base station must wait until the next ‘on’ cycle of the duty cycled radio before it will be able to receive a transmission and respond.
U.S. Pat. No. 9,656,621 teaches a system and method for sensor module power management powered by a solar energy harvester. They describe the use of a sensor to detect conditions when it may be desirable to turn on a vehicle sensor system radio to receive commands from a user device. Their system is brought to a mid power level to receive commands from the user device which would then bring operation to a high power level which could include transmission of sensor data at a high transmission rate. At a point when it is determined that the high power operation level is no longer necessary, the system changes to a low power level of operation, where a low power radio continues to receive commands from a user module, but in a manner that consumes minimal power. However, this low power state still must support the powering of at least a low performance radio, and therefore consumes power that causes the solar charged battery to deplete faster than desired.
The above difficulties and risks identify the need for a remote sensor system such as would be used in a vehicle imaging system that consumes virtually no power and responds without delay.